1. Field of the Invention
This invention relates to polyamide polyurethane polymers and is more particularly concerned with novel polyamide polyurethanes having a ketene-aminal as a recurring unit in the polymer network and the novel preparation of said polymers.
2. Description of the Prior Art
Polyurethane polymers and elastomers prepared from high molecular weight polyols and organic polyisocyanates and chain extended with low molecular weight polyols or polyamines have been known in the art for a long time; see U.S. Pat. No. 2,948,691, and Polyurethane Chemistry and Technology, Part II by J. H. Saunders and K. C. Frisch, Chapter IX, 1964, Interscience Publishers, New York, N.Y. for typical background art.
Polyurethane polymer properties have been varied in numerous ways by adjusting such parameters as reactant functionality, type of isocyanate or polyol, and, very importantly, by adjusting the amount and the type of extender employed. In some applications, particularly with the advent of very fast molding techniques such as the reaction injection molding (RIM) method, there is a need for very fast polymerization systems. However, more than just rapid polymerizations must be considered because other important factors are involved such as the amount of post cure treatment a molded sample requires to reach optimum physical properties, and, of course, the ultimate physical properties themselves. Generally speaking, the use of greater levels of, or, more active, polyurethane catalysts is not the answer. In fact, this latter approach usually results in adverse effects. In certain applications, a particularly important property is the amount of heat a molded sample can withstand before it will distort or begin to lose its molded configuration. This property is particularly important when molded automotive parts such as panels, doors, lids, fenders, etc. are exposed to high temperature paint drying ovens.
U.S. Pat. No. 4,218,543 has disclosed certain extender modifications (i.e. the use of specific active aromatic diamines) as one means of achieving a rapid urethane (RIM) process. The properties of the molded articles produced according to this method are good, including sufficient high temperature resistance to withstand paint oven-drying conditions. However, this method usually requires a post cure treatment of the molded polyurethanes at elevated temperatures in order for them to achieve their optimum operating physical property levels.
Surprisingly, we have now discovered that by employing a certain class of ketene-aminals as chain extenders that all of the above requirements can be met. Extremely rapidly reacting polyurethane polymers are obtained which are particularly suited to RIM methods of preparation. The ketene-aminals form amide linkages by direct reaction with the polyisocyanate component. Although polyamide linkages are formed in the polyurethane system according to the present invention, no volatile products are formed such as water, hydrohalic acids, carbon dioxide, or other volatile products which are produced in prior art methods for preparing polyamides, and which, if produced, would seriously interfere in any reaction molding process.
Unexpectedly, this provides the fastest and easiest means for forming polyamide linkages in conjunction with polyurethane linkages. At the same time, the advantageous physical properties such as good tensile and impact strengths, enjoyed by polyamides, are imparted to the polyamide polyurethanes in accordance with the present invention.
The degree of heat resistance of the polymers in accordance with the present invention can be easily controlled by the isocyanate index employed. That is to say, when a certain ratio of NCO to NCO reactive ingredients is exceeded and an isocyanate trimerization catalyst is present then polyisocyanurate linkages are incorporated into the polyamide polyurethane which gives rise to greater polymer heat resistance.
Most surprising and unexpected is the fact that the present polymers, notwithstanding their very high rate of formation, can be obtained in most cases in the as-molded form with their physical properties essentially at their optimum levels without the need of a post cure heat treatment.
Additionally, the molded samples have excellent "green strengths" which facilitate the demolding of complicated configurations, particularly those configurations with undercuts.